The modernization of metropolitans has provided urban residents with convenience and enjoyment; however the accompanied noise pollution has brought inconvenience and damages to residents. Although the state has explicitly stipulated the noise level of general residences in cities, that is 55 dB shall not be exceeded in the daytime, and 45 dB shall not be exceeded at night. However, the noise interference of urban centers and residential buildings on both sides of busy roads always exceeds this specified limit. In order to improve the noise interference of residential buildings of these areas, first the vehicles on roads shall be restricted, and second the microenvironment noise within residential buildings shall be controlled. Obviously, it's impossible to restrict the vehicles on roads, therefore, we can only consider improving the environment within residential buildings. For the existing technology, we normally install acoustic insulation devices, such as double glass and seal treatment, which can suppress the relatively low outdoor noises but can not do much to suppress louder noises. Consequently, we need to consider seeking out a suppression method adapted to environmental noises, so as to meet residents' housing requirements.
It is well known that the sounds sent from the same sound source can be turned into two-way sounds with opposite phases and corresponding amplitudes after technical processing, which will then generate the “silence” when being played in the same space. This theory has been proposed on U.S. Pat. No. 2,043,416 of American patent as far back as 1934. Later on, the products of “silencer” and “pilot headset” etc. come out in 1940s and 1950s. The sound transmission space of these products is very small. In addition, in order to prevent the sounds from being reflected in this small space, and make the phases of two-way inverted-phase sounds change relatively, the periphery of this space were pasted with acoustic materials. These technical measures are fundamentally unable to be applied to an apartment with only dozens of square meters. Moreover, due to the various aesthetic tastes of individuals, the decoration materials can not be used as excellent acoustic materials. Therefore, the technology feasible in very small space is not practical in a larger space.